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Recent developments in theory-based modelling of core heavy impuritytransport are presented, and shown to be necessary for quantitative descriptionof present experiments in JET and ASDEX Upgrade. The treatment of heavyimpurities is complicated by their large mass and charge, which result in astrong response to plasma rotation or any small background electrostatic fieldin the plasma, such as that generated by anisotropic external heating. Theseforces lead to strong poloidal asymmetries of impurity density, which haverecently been added to numerical tools describing both neoclassical andturbulent transport. Modelling predictions of the steady-state two-dimensionaltungsten impurity distribution are compared with experimental densitiesinterpreted from soft X-ray diagnostics. The modelling identifies neoclassicaltransport enhanced by poloidal asymmetries as the dominant mechanismresponsible for tungsten accumulation in the central core of the plasma.Depending on the bulk plasma profiles, neoclassical temperature screening canprevent accumulation, and can be enhanced by externally heated species,demonstrated here in ICRH plasmas.

Theoretical description of heavy impurity transport and its application to the modelling of tungsten in JET and ASDEX Upgrade